Vacuum pump

ABSTRACT

A vacuum pump including a centrifugal compressor stage on the side of a suction opening and a circumferential flow compressor on the side of an exhaust opening. The centrifugal compressor pump works as a Siegbahn pump at a steady state, and works as a centrifugal compressor under a transient condition at the initial stage of the pump operation, thus obtaining a high pumping speed under the transient condition.

BACKGROUND OF THE INVENTION

The present invention relates to a vacuum pump capable of evacuatinggaseous body from the atmospheric pressure to a high-vacuum and relatesmore particularly to a vacuum pump suitable for making a clean vacuum insemiconductor manufacturing apparatus.

Sputter ion pumps, turbomolecular pumps, cryo pumps, etc. have beenknown as conventional types of vacuum pumps. Any type of these pumpsrequires a roughing pump or a backing pump in order to evacuate air fromthe atmospheric pressure to a high-vacuum and they necessitatecomplicated controllers and the like for controlling the operation ofboth pumps, thus enlarging the size of the system using vacuum and theinstallation space for accommodating the system.

One known type of pump for enabling evacuation to be carried out fromthe atmospheric pressure to a high-vacuum has been proposed in U.S. Pat.No. 3,969,039 wherein pump is bilaterally symmetrical and is provided,in the housing, with a turbomolecular pump stage, a spiral moleculardrag pump stage, a centrifugal compressor stage and a vortex diode pumpstage located one after another from the side of a suction opening tothe side of exhaust opening.

The turbomolecular pump stage is composed of alternate combinations offixed plates attached to an inner wall of the housing and rotating discplates attached to the rotating shaft. The spiral molecular drag pumpstage is composed of alternate combinations of fixed plates attached toan inner wall of the housing and impellers in the form of disc platesattached to the rotating shaft. The centrifugal compressor stage iscomposed of alternate combinations of fixed plates with a diffuserattached to an inner wall of the housing and impellers attached to therotating shaft. The vortex diode pump stage is composed of alternatecombinations of fixed disc plates attached to an inner wall of thehousing and rotating disc plates attached to the rotating shaft.

The rotating shaft is driven through the medium of a turbine which isconnected to air inlet and air outlet ports formed in a side wall of thehousing.

A vacuum pump arranged as described above can effect satisfactorycompressing work when it reaches a steady state, the pressure at thesuction opening, that is, the ultimate pressure thereby beingsufficiently lowered. However, at the initial stage of the operation ofthe pump, that is a transient condition, the ppmp does not work at asufficient pumping speed. In such a transient condition, theturbomolecular pump stage and the spiral molecular drag pump stage whichare effective for the molecular flow air or the transition flow air donot substantially effect the compressing work because of the highpressure in the pump. The flow passage of the spiral molecular pumpstage has an especially small sectional area so as to have higherpressure ratio, thereby causing high pressure loss while at a high flowrate.

The object of the present invention is to provide a vacuum pump which iscapable of evacuating air from the atmospheric pressure to a high vacuumso as to obtain a clean vacuum and which can work at a high pumpingspeed under a transient condition at the initial stage of the pumpoperation.

To this end, the present invention provides a pump comprising a housinghaving suction and exhaust openings, a rotating shaft rotatablysupported in this housing, a plurality of fixed members attached to aninner wall of the housing, and a plurality of rotating members attachedto the rotating shaft, the fixed members and the rotating members beingalternately disposed so as to constitute pump stages in which acentrifugal compressor stage is constituted on the side of the suctionopening and a circumferential flow pump stage is constituted on the sideof the exhaust opening, with the rotating member of the centrifugalcompressor stage being composed of an open-form impeller having aplurality of backward vanes. This pump is designed to work as a Siegbahnmolecular pump in a steady state, and to work as a centrifugalcompressor under a transient condition of the initial pump operation,thus obtaining a high pumping speed under the transient condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional drawing showing the generalconstruction of a vacuum pump;

FIG. 2 is a cross-sectional view of a detail of a centrifugal compressorstage of FIG. 1;

FIG. 3 is a detail view taken along a line A--A in FIG. 2;

FIG. 4 is a detail view taken along a line B--B in FIG. 2

FIG. 5 is a cross-sectional view showing a detail of a circumferentialflow compressor stage;

FIG. 6 is a detailed view taken along a line C--C in FIG. 5; and

FIG. 7 is a detail view taken along a line D--D in FIG. 5.

DETAILED DESCRIPTION

Referring now to the drawings wherein like reference numerals are usedthroughout the various views to designate like parts and, moreparticularly, to FIG. 1, according to this figure, a vacuum pumpincludes a housing 1 having a suction opening 1A and an exhaust opening1B, a rotating shaft 3 rotatably supported by bearings 2 in the housing1, a centrifugal compressor stage 4 and a circumferential flowcompressor stage 5 placed one by one in the housing 1 from the suctionopening 1A to the exhaust opening 1B. The rotating shaft 3 is driven bya motor 6 connected thereto.

As shown in FIGS. 2 and 3, the centrifugal compressor stage 4 isprovided with open-form impellers each of which has a plurality ofbackward vanes 7 inwardly directed relative to the direction of rotationand is attached to the rotating shaft 3. The centrifugal compressorstage 4 is also provided with, as shown in FIGS. 2 and 4, a fixed discplate 4B attached to an inner wall of the housing 1 and has a pluralityof vanes 8 which are inwardly directed relative to the direction of therotation and which are located on a side facing the reverse side of theimpeller 4A, namely, the side on which the vanes 7 are not placed. Theopen-form impellers 4A and the fixed disc plate 4B are alternatelydisposed.

As shown in FIGS. 5 and 6, the circumferential compressor stage 5 isprovided with impellers 5A respectively attached to the rotating shaft 3and has a plurality of vanes 9 at the outer circumference thereof and isprovided with, as shown in FIGS. 5 and 7, fixed disc plates 5Brespectively attached to an inner wall of the housing 1 and havingU-shaped grooves 10 formed on one side thereof facing the surface of theimpellers 5A, namely, the side on which the vanes 9 are located, theimpellers 5A and the fixed disc plates 5B being alternately disposed. Anair passage 11 is formed at the end portion of the groove 10 by boring ahole 10a therein, as shown in FIGS. 5 and 7. A lublicating oil tank 12supplies lublicating oil to the bearings 2 through an oil passage formedin the rotating shaft 3.

Under a transient condition at the initial stage of the pump operation,the total inside pressure of the pump is substantially equal to theatmospheric pressure, and the condition of that gas flow is a viscousflow, so that the centrifugal compressor stage 4 works as a centrifugalcompressor. That is, the centrifugal compressor stage impeller 4Afunctions as a compressor impeller, and the flow passage formed betweenimpellers 4A and the vanes 8 of the fixed disc plate 4B functions as areturn channel for leading the flow from the outside diameter side tothe inside diameter side. As the impellers 4A effects the compressingwork, the centrifugal compressor stage 4 works as a compressor ratherthan a portion at which pressure loss occurs, thus discharging air at ahigh rate.

In a steady state where the compression ratio of the circumferentialflow compressor stage 5 becomes large and the pressure at the suctionopening of the circumferential flow stage becomes sufficiently lower,that is, in a steady state where this pressure is not more than about 6Torr, the condition of that gas flow is a transient flow or a molecularflow at the suction opening 1A of the pump, so that the centrifugalcompressor works as a Siegbahn molecular pump. That is, the impeller 4A,having the vanes 7, functions as a rotating disc plate with helicalgrooves and works as a Siegbahn molecular pump which effects compressingwork in combination with the reverse side of the impeller 4A, namely,the side on which the vanes 7 are not located.

In the steady state, the bulk flow rate is substantially zero, since aquantity of gas which flows into the circumferential flow compressorstage 5 has been sufficiently compressed by the centrifugal compressorstage 4. Then, the circumferential flow compressor stage 5 is operatedsubstantially at zero capacity, and reaches the ultimate low pressurethrough a small number of members thereof because of the characteristicof circumferential flow compressors enabling a high compression ratio tobe obtained at zero capacity.

The number of members and the rotational speed of the centrifugalcompressor stage 4 and the circumferential flow compressor stage 5 areset such that, in a steady state of operation, the pressure at theboundary between both stages corresponds to the point of change betweenthe viscous flow and the transient flow. Generally, a combination of thecentrifugal compressor stage of one to three members and thecircumferential flow compressor stage of six to ten members assures thepressure of 10⁻³ to 10⁻⁴ Torr.

According to the present invention, as described above, the centrifugalcompressor stage works as a centrifugal compressor under a transientcondition and works as a Siegbahn molecular pump in a steady state,thereby providing a double effect, so that, under condition that thepressure at the exhaust opening is maintained at atmospheric pressure, aclean vacuum can be obtained at the suction opening. Moreover, under atransient condition at the initial stage of the pump operation, the pumpcan work at a high pumping speed.

What is claimed is:
 1. A vacuum pump comprising: a housing includingsuction and exhaust openings, a rotating shaft rotatably supported insaid housing, a plurality of fixed members attached to an inner wall ofsaid housing, and a plurality of rotating members attached to saidrotating shaft, said fixed members and said rotating members beingdisposed alternately so as to form pump stages in which a centrifugalcompressor stage is formed on a side of said suction opening and acircumferential flow pump stage is formed on a side of said exhaustopening, said rotating member of said centrifugal compressor stageincluding open-form impellers having a plurality of backward vanes, andwherein said fixed member of said centrifugal compressor stage includesa fixed disc plate with a plurality of vanes disposed so as to face areverse side of said impeller and inwardly directed relative to thedirection of rotation at an outside diametral portion of said fixedmember.
 2. A vacuum pump comprising: a housing including suction andexhaust openings, a rotating shaft rotatably supported in said housing,a plurality of fixed member attached to an inner wall of said housing,and a plurality of rotating members attached to said rotating shaft,said fixed members and said rotating members being disposed alternatelyso as to form pump stages in which a centrifugal compressor stage isformed on a side of said suction opening and a circumferential flow pumpstage is formed on a side of said exhaust opening, said rotating memberof said centrifugal compressor stage including open-form impellershaving a plurality of backward vanes, and wherein a diameter of saidcircumferential flow compressor stage on a side of said exhaust openingis smaller than a diameter thereof on a side of said suction opening. 3.A vacuum pump according to claim 2, comprising: a housing includingsuction and exhaust openings, a rotating shaft rotatably supported insaid housing, a plurality of fixed member attached to an inner wall ofsaid housing, and a plurality of rotating members attached to saidrotating /shaft, said fixed members and said rotating members beingdisposed alternately so as to form pump stages in which a centrifugalcompressor stage is formed on a side of said suction opening and acircumferential flow pump stage is formed on a side of said exhaustopening, said rotating member of said centrifugal compressor stageincluding open-form impellers having a plurality of backward vanes, andwherein a diameter of said circumferential flow compressor stage on aside of said exhaust opening is smaller than a diameter thereof on aside of said suction opening. .Iadd.
 4. A vacuum pump comprising: ahousing including a suction and exhaust openings, a rotating shaftrotatably supported in said housing, a plurality of fixed membersattached to an inner wall of said housing, and a plurality of rotatingmembers attached to said rotating shaft, said fixed members and saidrotating members being disposed alternately so as to form pump stages inwhich a centrifugal compressor stage is formed on a side of said suctionopening and a circumferential pump stage is formed in a side of saidexhaust opening, said rotating member of said centrifugal compressorstage including impellers having a plurality of backward vanes, andwherein said fixed member of said centrifugal compressor stage includesthe fixed disc plate with a plurality of vanes disposed so as to facethe reverse side of said impeller and inwardly directed relative to thedirection of rotation of an outside diametral portion of said fixedmember. .Iaddend. .Iadd.5. A vacuum pump comprising: a housing includinga suction and exhaust openings, a rotating shaft rotatably supported insaid housing, a plurality of fixed members attached to an inner wall ofsaid housing, and a plurality of rotating members attached to saidrotating shaft, said fixed members and said rotating members beingdisposed alternately so as to form pump stages in which a centrifugalcompressor stage is formed on a side of said suction opening and acircumferential flow pump stage is formed in a side of said exhaustopening, said rotating member of said centrifugal compressor stageincluding impellers having a plurality of backward vanes, and wherein adiameter of said circumferential flow compressor stage on a side of saidexhaust opening is smaller than a diameter thereof on a side of saidsuction opening. .Iaddend. .Iadd.6. A vacuum pump according to claim 5,comprising a housing including suction and exhaust openings, a rotatingshaft rotatably supported in said housing, a plurality of fixed membersattached to an inner wall of said housing, and a plurality of rotatingmembers attached to said rotating shaft, said fixed members and saidrotating members being disposed alternately so as to form pump stages inwhich a centrifugal compressor stage is formed on a side of said suctionopening and a circumferential flow pump stage is formed on a side ofsaid exhaust opening, said rotating member of said centrifugalcompressor stage including impellers having a plurality of backwardvanes, and wherein a diameter of said circumferential flow compressorstage on a side of said exhaust opening is smaller than a diameterthereof on a side of said suction opening. .Iaddend. .Iadd.7. A vacuumpump having a housing including a suction opening and an exhaust openingand a pump stage disposed in said housing, said pump stage comprising:acentrifugal compressor stage means disposed on a side of the suctionopening in said housing for obtaining a high compression ratio in amolecular flow and an intermediate flow region and then generating acompressive operation in a viscous flow region, a circumferential flowpump stage means disposed on a side of said exhaust opening in saidhousing for obtaining a high compression ratio in the viscous flowregion, and a rotating shaft means disposed between said centrifugalcompressor stage means and circumferential flow pump stage means..Iaddend. .Iadd.8. A vacuum pump according to claim 7, wherein thecentrifugal compressor stage means includes impeller means attached tothe rotating shaft means, a fixed disc plate means attached to an innerwall of the housing and including a plurality of vanes inwardly directedrelative to said direction of rotation and disposed on a reverse side ofsaid impeller means. .Iaddend. .Iadd.9. A vacuum pump according to claim8, wherein said impeller means and said fixed disc plate means arealternately arranged. .Iaddend. .Iadd.10. A vacuum pump according toclaim 9 wherein said impeller means includes a plurality of backwardvanes. .Iaddend.